1. Field of the Invention
The present invention is directed to a tape cartridge which contains magnetic recording tape, in particular a cartridge containing an extremely wide tape which allows fast access time to data recorded on the tape, as well as a drive unit for such a tape cartridge.
2. Description of the Prior Art and Related Subject Matter
The use of Magnetic tape as a medium for data recording has the significant advantages of a relatively low cost and a relatively large recording surface area. Nevertheless, conventional magnetic tape has certain disadvantages associated therewith.
A first of these disadvantages is that tape is a sequential medium, which means that when a data transfer head is located at a beginning of a tape, it is necessary for the tape to be transported along its entire length in order to retrieve (or re-write) information at the end of the tape.
A second disadvantage is that, due to the desire and necessity of storing as much data as possible within an available tape area, the data transfer head technology as well as the recording media technology are pushed to their quality limits.
Moreover, many existing drives and cartridges must be designed within specified form factors, in order to satisfy standardization requirements. As an increasing number of functions become available, which are desired to be accommodated in a drive or on a tape, data storage area or other functions must be sacrificed to accommodate the new, additional functions, or some type of compromise must be reached in the overall design.
Among the more important market requirements which are expected in the near future for data storage on tape is that the need for higher storage capacity will continue to increase, at an even faster rate than previously. As discussed below, for example, the storage capacity of a currently available single cartridge is not sufficient for unattended backup during a longer period of time, and therefore so-called autoloader systems have been developed to automatically insert and remove a number of cartridges in a sequence.
Further market requirements are expected to be a need for faster time to access data, a need for an increased data transfer rate, a lower cost per MB (megabyte) and an overall improved quality and reduced cost.
As noted above, the limited data storage capacity of conventional cartridges has resulted in the development of autoloader systems. Conventional autoloader systems, however, are not a satisfactory solution to the problem of storing a large amount of data in an unattended backup procedure over a relatively long period of time. Several disadvantages exist with regard to currently available autoloader systems.
Because such autoloader systems make use of a large number of cartridges, the cartridges are made relatively small, and therefore have a limited space available for use for data storage. Typically, six to ten of such cartridges must be put in a magazine in order to have sufficient storage area (capacity). Because of the relatively small size of the cartridges, the drive is also made small, in order to match standardized form factors. The drive is disposed in a system housing, which also contains robotics, electronics and software needed for loading an unloading the cartridges.
The relatively large number of components, and therefore the relatively high cost, associated with conventional autoloader systems makes the use of such systems an unattractive alternative for a customer who merely wants long term data backup.
To address these problems, a tape cartridge and a drive for extremely wide tape are disclosed in co-pending U.S. application Ser. No. 691,165, filed Oct. 19, 2000, the teachings of which are incorporated herein by reference. The tape cartridge and drive described therein accommodate tape having an extremely wide width, such as a width that is greater than approximately 24 mm, or in a range between approximately 24 mm and approximately 127 mm.
The width of this extremely wide tape, therefore, is greater than that of a conventional magnetic recording tape by a factor of 6 to 10 times. Because the tape has this extremely wide width, the total tape length can be made significantly shorter while still making the same total area available for data storage. Making the tape shorter, however, requires less time for winding and unwinding the tape from the hubs on which it is carried in order to access data at a particular location on the tape.
It is important, however, that the housing for accommodating such extremely wide tape have the same, or substantially the same, form factor as conventional recording cartridges, so as to be accommodated in the openings for conventional tape cartridges in tape drives and auto loaders and magazines. This means that the axes of rotation of the tape hubs in cartridges for accommodating extremely wide tape will proceed parallel to a xe2x80x9clongerxe2x80x9d dimension of the cartridge housing, rather than perpendicular to the shortest dimension (height) as in a conventional cartridge housing. Given a length of extremely wide tape which is necessary to provide the same total area available for recording data on the tape as a conventionally sized tape, such a length of extremely wide tape can be accommodated in a housing having a height which is comparable to the height of a conventional tape cartridge only when the tape is substantially evenly distributed in respective tape packs on the two hubs in the housing. When any significant amount of extremely wide tape is wound onto one of the hubs, the diameter on the tape pack on that hub increases beyond the standard height of a conventional cartridge housing.
This problem could be addressed by simply providing a lesser length of extremely wide tape in the cartridge, so that even when all of the tape is wound on one tape hub in one tape pack, the diameter of that tape pack still would not exceed the height of a standard tape cartridge.
This would defeat one of the advantages of employing extremely wide tape, however, by decreasing the total area available for recording data.
It therefore remains a problem in the art to provide a tape cartridge which accommodates an amount of extremely wide tape therein having a total area available for data recording which is substantially the same as the area available for data recording in a conventional tape cartridge, and which has a form factor which is substantially the same as the form factor for a conventional tape cartridge.
It is an object of the present invention to provide a recoding tape cartridge which accommodates a length of extremely wide recording tape having a reduced access time to data in comparison to a conventional recording tape with the same area available for data recording, and which is contained in a tape cartridge having a form factor which is substantially the same as that of a standard tape cartridge.
The above object is achieved in accordance with the principles of the present invention in a recording tape cartridge having a housing with two tape hubs rotatably mounted therein, the tape hubs having magnetic recording tape wound thereon for winding and unwinding between the two hubs in a tape transport direction, and wherein the housing is composed of first and second housing parts which are movable relative to each other in a direction perpendicular to the tape transport direction so as to expand the housing in the direction perpendicular to the tape transport direction to accommodate an increase in diameter of the tape pack on one of the hubs which arises as the extremely wide tape is wound onto that hub.
The inventive recording tape cartridge has a form factor with a low height so that the cartridge can be inserted into the access door opening in conventional tape drives. As an example, the cartridge can have a form factor of four inches by five inches and a height of one inch, which is very similar to single reel cartridges currently in use. The tape surface area will be approximately the same as in such a conventional single reel cartridge, but the length of the extremely wide tape will be reduced approximately by a factor of eight, so that the access time to data on the extremely wide tape is significantly reduced.
In an embodiment, expansion of the relatively movable parts of the housing is accomplished by an expansion mechanism contained in the housing. The expansion mechanism can have gripper portions which are accessible from an exterior of the tape cartridge, which can be gripped by the mechanism which pulls the tape cartridge into a tape drive. Guide channels on opposite sides of the tape drive immediately inside the access door hold the two housing parts together in their initial, low height positions, but once the cartridge has been pulled sufficiently far into the tape drive, the guide channels either cease or expand so as to allow the expansion mechanism, being pulled on by the grippers, to expand the housing parts once the cartridge has cleared the access door.
In a further embodiment, a tape positioning mechanism can also be provided inside the cartridge, having pivotable elements connected to one of the housing parts. As the cartridge is pulled into the drive and the read/write head of the drive is inserted into the cartridge before it expands, the tape positioning mechanism keeps the tape away from the read/write head during insertion thereof, thereby avoiding damage to the tape. When the cartridge clears the access door and is allowed to expand, the tape positioning mechanism then brings the tape into contact with the write/read head, for recording data on the tape or reading data therefrom.
In a further embodiment, the end of the cartridge which proceeds first into the drive has a normally closed door therein, which is hinged to one of the housing parts at one side of the door. The opposite side of the door has small protrusions thereon which engage correspondingly shaped openings in the other housing part. When the door is in the closed position, therefore, it retains the housing parts together by virtue of the protrusions fitting into the openings. As the cartridge is pulled into the drive and the read/write head pushes the door open so that it pivots at its hinge, the protrusions no longer remain in the openings thereby allowing the housing parts to move relative to each other, so that the housing can expand.